The vibrating beam accelerometer is basically a crystal oscillator whose frequency is made to be a systematic function of acceleration. The vibrating beam accelerometer incorporates a quartz vibrating beam force transducer, such as is described and claimed in U.S. Pat. No. 3,470,400 which issued Sept. 30, 1969; and in U.S. Pat. No. 3,479,536, which issued Nov. 18, 1969, both of which are assigned to the present Assignee.
The vibrating beam accelerometer is advantageous in that it is inherently a high precision measuring instrument which has an extremely large dynamic range. The vibrating beam accelerometer is susceptible to a fully solid state mechanization having no moving parts. Moreover, the accelerometer may be constructed to be small and compact, and at a relatively low cost.
However, since quartz is a brittle material, the resonator in the prior art vibrating beam accelerometer is susceptible to breakage from overload forces. These overload forces occur when the proof mass of the vibrating beam accelerometer is subjected to excessive handling shocks or input accelerations. Accordingly, an important objective of the present invention is to provide a vibrating beam accelerometer which is constructed such that the quartz resonator is protected from overload forces.
No such protective mechanism is provided in the prior art vibrating beam accelerometers, and the only way in which the resonator force loading may be maintained to a tolerable level in the presence of excessive handling shocks and excessively high input accelerations is to limit the proof mass of the accelerometer to a relatively low value. However, when the proof mass is relatively low, a substantial portion of the resonator force measuring range goes unused, for many applications. The construction of the vibrating beam accelerometer of the present invention, on the other hand, is such that the entire input range of the resonator is usable, up to the threshold at which the protective mechanism in the accelerometer becomes operative.